Silicon carbide (SiC) is rarely found in nature. It has, however, been manufactured for more than eighty years, in crystalline form, for abrasive products. Silicon carbide crystals found in nature and in abrasive products are generally black and not translucent because they contain substantial levels of impurity atoms.
In the 1950's the Lely process was developed at General Electric Company by which silicon carbide was sublimed and randomly deposited to produce small, thin silicon carbide crystals that were used in early silicon carbide semiconductor device development.
Because of the theoretically quite favorable electronic properties of silicon carbide, significant development activities were initiated during the 1960's and 1970's with the objective of growing large (bulk) crystals of low impurity silicon carbide for use in the production of semiconductor devices. These efforts finally resulted in the commercial availability of relatively low impurity, translucent silicon carbide crystals.
North Carolina State University was issued U.S. Pat. Nos. 4,866,005 and Re. 34,861 on the growth of single crystal silicon carbide through a sublimation process. The disclosure of U.S. Pat. Nos. 4,866,005 and Re. 34,861 are incorporated herein by reference as if set forth fully herein. Since that time, the growth of silicon carbide crystals has been described in several U.S. Patents, including commonly assigned U.S. Pat. No. 6,045,613 entitled “PRODUCTION OF BULK SINGLE CRYSTALS OF SILICON CARBIDE,” the disclosure of which is incorporated herein by reference as if set forth fully herein. Additional patents relating to the growth of silicon carbide or silicon carbide alloys include commonly assigned U.S. Pat. No. 6,048,813 entitled “SIMULATED DIAMOND GEMSTONES FORMED OF ALUMINUM NITRIDE AND ALUMINUM NITRIDE: SILICON CARBIDE ALLOYS,” and U.S. Pat. No. 6,086,672 entitled “GROWTH OF BULK SINGLE CRYSTALS OF ALUMINUM NITRIDE: SILICON CARBIDE ALLOYS,” the disclosures of which are incorporated herein by reference as if set forth fully herein.
One difficulty with silicon carbide is that silicon carbide may contain micropipes or other defects, such as dislocation defects. Such defects may reduce the suitability of regions of a silicon carbide wafer containing such defects for use in a semiconductor device. For example, a transistor with such defects incorporated therein may have a higher leakage current than a corresponding transistor without such defects. Accordingly, improvements may be needed in the growth of silicon carbide crystals.
In gallium arsenide (GaAs) and gallium nitride (GaN) growth through chemical vapor deposition (CVD), epitaxial lateral overgrowth (ELOG) and pendeo-epitaxial growth techniques have been utilized to reduce defects in layers of GaAs or GaN. Such techniques are, for example, illustrated in U.S. Pat. No. 4,522,661. U.S. Pat. No. 6,051,849 and U.S. Pat. No. 6,177,688. However, growth of silicon carbide crystals (e.g. boules) suitable for providing wafers or substrates is typically not carried out using CVD processes but is performed using physical vapor transport (PVT) growth, such as through a sublimation growth process as described above.